When viewing diffs in Foreman, such as filebucket diffs in puppet reports, or history diffs in provisioning templates et al, added lines show up in black, and removed lines show up in green. Also, these two colors are reversed for the + and - symbols prefixing the lines (+ in green, - in black).

I suggest using green for additions (+), red for removals (-), and using the same color for the prefix symbol as the rest of the line.